Good news guys. Opera has made their stance clear in a statement to ZDNET. I have posted a link to the article below to read it in full.

"ZDNet also received a similar statement from Opera, another browser vendor which uses the Chromium codebase.

"We might also consider keeping the referenced APIs working, even if Chrome doesn't, but again, this is not really an issue for the more than 300 million people who have chosen Opera," an Opera spokesperson told us.

This is because, just like Brave, Opera also ships with a built-in ad blocker.

"All the Opera browsers, both on mobile and PC, come with an ad blocker that users can choose to enable," the spokesperson said. "This means that Opera users aren't really exposed to these changes - unlike users of most other browsers."

A fair number of sites already block ad-blocking browsers/extensions. Whether an ad-favoring site sniffs a user agent string for browser type or uses site code to sniff for ad blocking, the result turns out to be essentially the same: up pops a usage-blocking message if ads can be user-blocked. The struggle is really over how websites can recoup their costs of providing their online services/media, and until that is finally settled somehow, this stands as only one more round of tactics.

I really hate it when browser devs use the "we have our own adblock, built in and this will stay" as an advantage.
Who considers opera's built in adblock to be a good one? Because I don't.

Proof

Both those screenshots are from facebook's ads and were taken the first days I started using chromium opera, back in early 2017, with no extra extensions yet.
The first one shows the original ad frame and no adblock at all, and the second one shows the same frame with opera's built in adblock. As it seems, all opera's adblock did was to filter the "Sponsored" word on the top and nothing more.
And that was the moment I disabled it and installed ublock origin to opera too.

At this point in time, it's way too early to know how this will unfold for various browsers, Opera included. At least in part, that's because the final version of the new chromium API and any 'permanent' changes/deprecation of the old API have not been decided upon. Only then, and based upon that impact to browser coding, will it be possible to determine how the various browsers will be impacted. Those impacts will determine the economics or possibility of various browsers preserving existing ad-blocking capabilities or extension compatibility. Right now, it appears that everyone's at the mercy of how the chromium changes are actually implemented, and that's where the battle is being fought between app and chromium developers.